A ball joint for movably connecting shaft-like components to each other is conventionally used in suspensions and steering mechanisms for vehicles such as automobiles. In general, a ball joint is primarily constituted such that a spherical ball portion formed on an end portion of a shaft-like ball stud is slidably received in a cylindrical socket having a bottom through a ball seat (also referred to as a “bearing seat”) formed of resin.
In such a ball joint, as shown in below-listed Patent Document 1, in order to prevent entry or invasion of foreign substances such as water droplets and dust into the socket in which the ball portion slidingly moves and to prevent leakage of grease charged into the socket, a dust cover is provided to cover an opening portion of the socket. This dust cover is formed of an elastically deformable material (e.g., a rubber material) and has generally a cylindrical tubular shape. One open end portion of the dust cover is fitted onto the outer periphery of the opening portion of the socket, and the other open end portion of the dust cover is fitted onto the outer periphery of the ball stud. In order to prevent the dust cover from coming off and to prevent entry of foreign substances into a region where the dust cover is mated with the socket, a retaining ring is fitted onto the dust cover in order to tighten the outer periphery of the dust cover which is fitted onto the outer periphery of the socket.